His invention
ran in two great grooves, one based upon the science of heat, the other
based upon the science of electricity; and the electric thermometer was,
as it were, a delicate cross-coupling which connected both. Siemens
might have been two men, if we are to judge by the work he did; and
either half of the twin-career he led would of itself suffice to make an
eminent reputation.
The success of his metallurgical enterprise no doubt reacted on his
telegraphic business. The making and laying of the Malta to Alexandria
cable gave rise to researches on the resistance and electrification of
insulating materials under pressure, which formed the subject of a paper
read before the British Association in 1863. The effect of pressure up
to 300 atmospheres was observed, and the fact elicited that the
inductive capacity of gutta-percha is not affected by increased
pressure, whereas that of india-rubber is diminished. The electrical
tests employed during the construction of the Malta and Alexandria
cable, and the insulation and protection of submarine cables, also
formed the subject of a paper which was read before the Institution of
Civil Engineers in 1862.
It is always interesting to trace the necessity which directly or
indirectly was the parent of a particular invention; and in the great
importance of an accurate record of the sea-depth in which a cable is
being laid, together with the tedious and troublesome character of
ordinary sounding by the lead-line, especially when a ship is actually
paying out cable, we may find the requirements which led to the
invention of the 'bathometer,' an instrument designed to indicate the
depth of water over which a vessel is passing without submerging a line.
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